Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $64.92   10.369%   $71.6516   $71.65   $71.65   $71.70  
  Purchase #2 $146.53   12.384%   $164.6763   $164.68   $164.70   $164.70  
  Purchase #3 $235.67   12.426%   $264.9544   $264.95   $264.95   $265.00  
  Purchase #4 $204.41   11.382%   $227.6759   $227.68   $227.70   $227.70  
  Purchase #5 $51.89   4.799%   $54.3802   $54.38   $54.40   $54.40  
  Purchase #6 $19.68   9.695%   $21.588   $21.59   $21.60   $21.60  
  Purchase #7 $208.37   7.860%   $224.7479   $224.75   $224.75   $224.70  
  7 purchase totals = $931.47       $1,029.6743   $1,029.68   $1,029.75   $1,029.80